The polymerization of styrene and maleic anhydride by free radical initiation is well known in the prior art. Similarly, poly(styrene-co-maleic anhydride) and poly(styrene-alt-maleic anhydride) polymers are well known. Further, imidization between a maleic anhydride and a primary amine group is a commonly known chemical reaction. Publications which have recognized these reactions include: German Patent DE 4241538, assigned to Leuna-Werke A. -G; Japanese Patent JP 94248017, assigned to Monsanto Kasel Kk.; and, Italian Patent EP 322905 A2, assigned to Montedipe S.p.A. Various other non-patent publications have also recognized these reactions. Included among them are: L. E. Colleman, Jr., J. F. Bork, and H. Donn, Jr., J. Org. Chem., 24, 185(1959); A. Matsumoto, Y. Oki, and T. Otsu, Polymer J., 23(3), 201(1991); L. Haeussler, U. Wienhold, V. Albricht, and S. Zschoche, Themochim. Acta, 277, 14(1966); W. Kim, and K. Seo, Macromol. Rapid Commun., 17, 835(1996); W. Lee, and G. Hwong, J. Appl. Polym. Sci., 59, 599(1996); and, I. Vermeesch and G. Groeninckx, J. Appl. Polym. Sci., 53, 1356(1994).
The synthesis of monofunctional N-alkyl and N-aryl maleimides are also well known in the prior art. They have been extensively used to improve the heat stability of homopolymers and especially copolymers prepared from vinyl monomers. Typically, the bulk resins comprise ABS (poly-(acrylonitrile-co-butadiene-co-styrene)) or a polyblend of poly-(acrylonitrile-co-butadiene) and poly-(styrene-co-acrylonitrile); PVC (poly(vinyl chloride)); SAN (poly(styrene-co-acrylonitrile)); PMMA (poly-(methyl methacrylate)); and the like. The maleimides can be copolymerized with other monomers such as acrylonitrile, butadiene, styrene, methyl methacrylate, vinyl chloride, vinyl acetate and many other comonomers. A more preferred practice in the industry is to produce copolymers of maleimides with other monomers such as styrene and optionally acrylonitrile and to blend these with ABS and SAN resins. In any event, the polymer compositions are adjusted so that the copolymers are fully compatible with the bulk resins (e.g., ABS and/or SAN) as shown by the presence of a single glass transition point (Tg) as determined by differential scanning calorimetry (DSC).
It has long been recognized that two or more polymers may be blended together to form a wide variety of random or structured morphologies to obtain products that potentially offer desirable combinations of characteristics. However, it may be difficult or even impossible in practice to achieve many potential combinations through simple blending because of some inherent and fundamental problem. Frequently, the two polymers are thermodynamically immiscible, which precludes generating a truly homogeneous product. This immiscibility may not be a problem per se since often it is desirable to have a two-phase structure. However, the situation at the interface between these two phases very often does lead to problems. The typical case is one of high interfacial tension and poor adhesion between the two phases. This interfacial tension contributes, along with high viscosities, to the inherent difficulty of imparting the desired degree of dispersion to random mixtures and to their subsequent lack of stability, giving rise to gross separation or stratification during later processing or use. Poor adhesion leads, in part, to the very weak and brittle mechanical behavior often observed in dispersed blends and may render some highly structured morphologies impossible.
The abrasion resistance of rubbers generally increases with increasing molecular weight. However, viscosity of the unvulcanized rubber also increases with increase in molecular weight. Accordingly, in conventional practice a plasticizer (xe2x80x9cextending oilxe2x80x9d) is added to the unvulcanized rubber to lower its viscosity and to increase its workability to a point suitable for extrusion or other processing.
Kent et al in U.S. Pat. No. 3,528,936 and Cowperthwaite et al in U.S. Pat. No. 3,751,378 recognize that high molecular weight polymers of butadiene, etc., may be plasticized by addition of certain polyester monomers. Both patents teach admixture of the monomer and polymer together with an inorganic filler and other ingredients on an open mill or in an internal mixer, i.e., xe2x80x9cdryxe2x80x9d blending with a filler.
It is particularly desirable to prepare a polymer useful as an oil substitute that performs the function of a polymer extender or plasticizer while enhancing beneficial polymer properties such as tensile strength, maximum elongation, tear strength, damping properties.
It is an object of this invention to produce a poly(maleimide-co-alkenyl benzene) xe2x80x9ccentipedexe2x80x9d polymer formed by imidizing a poly(alkenyl benzene-co-maleic anhydride). The xe2x80x9ccentipedexe2x80x9d polymer has a high molecular weight spine connected with many relatively short side chains. The length of the main chain usually equals or is longer than the entanglement length, which is herein defined theoretically as an order of magnitude of 100 repeating units, while the length of the side chains is much smaller than the entanglement length.
Still more specifically, it is an object of the invention to provide a centipede polymer formed by imidizing a poly(styrene-co-maleic anhydride) with a primary amine to form a poly(maleimide-co-styrene) polymer.
It is a further object of the present invention to produce a high molecular weight poly(maleimide-co-alkenyl benzene) polymer formed by the reaction product of a maleic anhydride contributed monomer unit of a poly(alkyl benzene-co-maleic anhydride) and a primary amine containing from 1 to 50 carbon atoms in the alkyl and alkoxy substituents in the primary amine.
It is another object of the invention is to produce a high molecular weight poly(maleimide-co-alkenyl benzene) polymer useful as an oil substitute to be used as an a polymer extender that enhances beneficial polymer properties such as tensile strength, maximum elongation, tear strength, damping properties, and the like.
Finally, it is yet another object of the invention is to produce a centipede polymer that exhibits improved properties such as tensile strength, maximum elongation, tear strength, damping properties, and the like; that can be employed as a substitute for oils and/or plasticizers in the production of various other rubber compounds.
The present invention is broadly directed to poly(maleimide-co-alkenyl benzene) centipede polymer compositions formed by reacting a poly(alkenyl benzene-co-maleic anhydride) with a primary amine. It is further directed to a process for blending the poly(maleimide-co-alkenyl benzene) centipede polymer with elastomeric polymers, in combination with, or in substitution of, conventional extender oils, to produce extended polymers having improved properties such as tensile strength, maximum elongation, tear strength, damping properties, and the like.
The present invention is broadly directed to a polymer compositions of a poly(alkenyl benzene-co-maleimide) formed by reacting a poly(alkyl benzene-co-maleic anhydride) with a primary amine.
For the purposes of this invention, poly(alkenyl benzene-co-maleimide) and poly(alkyl benzene-co-maleic anhydride) are defined to encompass random and stereo-specific copolymers, including copolymers having alternating alkenyl benzene and maleimide or maleic anhydride contributed monomer units along the polymer backbone. Such alternating structure are typically described as poly(alkenyl benzene-adj-maleimide) and poly(alkyl benzene-adj-maleic anhydride), however, these polymers are encompassed herein within the descriptions poly(alkenyl benzene-co-maleimide) and poly(alkyl benzene-co-maleic anhydride)
Processes for forming poly(alkyl benzene-co-maleic anhydride) polymers are well known to those skilled in the art. The preparation of the copolymers from electron donor monomers, such as styrene, and electron acceptor monomers, such as maleic anhydride, as a result of complexation of the electron acceptor monomers may be carried out in the absence as well as in the presence of an organic free radical initiator in bulk, or in an inert hydrocarbon or halogenated hydrocarbon solvent such as benzene, toluene, hexane, carbon tetrachloride, chloroform, etc. (N. G. Gaylord and H. Antropiusova, Journal of Polymer Science, Part B, 7, 145 (1969) and Macromolecules, 2, 442 (1969); A. Takahashi and N. G. Gaylord, Journal of Macromolecular Science (Chemistry), A4, 127 (1970).
Poly(alkyl benzene-co-maleic anhydride) polymers are prepared by reacting monomers of alkenylbenzene with maleic anhydride. The preferred alkenyl benzene monomers used for forming the poly(alkyl benzene-co-maleic anhydride) polymer are styrene or xcex1-methylstyrene. Suitable, but less preferred substitutes are: p-methylstyrene, 4-phenylstyrene, m-methylstyrene, o-methylstyrene, p-tert-butylstyrene, dimethylstyrene, and combinations thereof.
The poly(alkyl benzene-co-maleic anhydride) for use in the present invention is a polymer containing from about 5 to 99 mole percent of maleic anhydride monomer with the remainder being alkyl benzene monomer. The preferred poly(alkyl benzene-co-maleic anhydride) contains from 20 to 50 mole percent of maleic anhydride monomer. The most preferred poly(alkyl benzene-co-maleic anhydride) for use in the present invention is poly(styrene-co-maleic anhydride) containing 50 mole percent of maleic anhydride monomer and 50 mole percent of styrene monomer. The comonomers, maleic anhydride and alkenyl benzene, can be randomly or alternatingly distributed in the chain, however, it is preferred to have these comonomers alternating along the polymer backbone chain.
The poly(alkenyl benzene-co-maleic anhydride) has a molecular weight range between about 1,000 and up to about 500,000 or higher, more typically between about 10,000 and 500,000, and even more typically between about 150,000 and 450,000, where the molecular weight is weight-average (xe2x80x9cMwxe2x80x9d).
The poly(maleimide-co-alkenyl benzene) of the instant invention is formed by reacting a poly(alkyl benzene-co-maleic anhydride) in the presence of a mono-primary amine at a temperature from about 100xc2x0 C. to about 300xc2x0 C. and at a pressure from about slightly above vacuum to about 20 atmospheres, under substantially dry conditions. The reactants are preferably dry mixed in the absence of solvents in a suitable mixing apparatus such as a Brabender mixer equipped with Banbury blades. It is preferable to purge the mixer with nitrogen prior to the charging of the reactants. The primary amine may be added in a singular charge or in sequential partial charges into a reactor containing a charge of poly(alkyl benzene-co-maleic anhydride). Preferably the primary amine is charged in ratio between 0.8 to 1.0 of moles of amine per monomer contributed units of maleic anhydride in the poly(alkyl benzene-co-maleic anhydride).
Suitable primary amine include but are not limited to: alkyl amines; alkyl benzyl amines; alkyl phenyl amines; alkoxybenzyl amines; alkyl aminobenzoates; alkoxy aniline; and other linear primary amines containing from 1 to 50 carbon atoms, preferably 6 to 30 carbon atoms, in the alkyl and alkoxy substituents in these primary amines. It is understood that the alkyl and alkoxy substituents on the above discussed primary amines can be linear or branched, preferably linear, and saturated or unsaturated, preferably saturated. Exemplary, but not exclusive of such amines are: hexylamine, octylamine, dodecylamine and the like.
The poly(maleimide-co-alkenyl benzene), preferably has a molecular weight range between about 1,000 and up to about 500,000 or higher, more typically between about 10,000 and 500,000, and even more typically between about 150,000 and 450,000, where the molecular weight is weight-average (xe2x80x9cMwxe2x80x9d).
The poly(maleimide-co-alkenyl benzene) centipede polymers of the present invention can be employed as high damping additives and as an alternative for plasticizers or oils in the formulation of various rubber compounds or elastomeric polymers.
The centipede polymer of the present invention may be prepared by any means well known in the art for combining such ingredients, such as blending, milling or internal batch mixing. A rapid and convenient method of preparation comprises heating a mixture of the components to a temperature of about 50xc2x0 C. to about 290xc2x0 C.
The centipede polymers of this invention are preferably manufactured by mixing and dynamically heat-treating the components described above, namely, by melt-mixing. As for the mixing equipment, any conventional, generally known equipment such as an open-type mixing roll, closed-type Banbury mixer, closed type Brabender mixer, extruding machine, kneader, continuous mixer, etc., is acceptable. The closed-type Brabender mixer is preferable, and mixing in an inactive gas environment, such as nitrogen or carbon dioxide, is also preferable.
In accordance with the present invention, the centipede polymer composition of the present invention may be added as an extender or as a plasticizer to an elastomeric polymer in an amount ranging from about 0.5-200 parts by weight per 100 parts by weight of a solid elastomeric polymer; preferably in an amount ranging from about 0.1 to about 50 parts by weight of centipede polymer per 100 parts by weight of the elastomeric polymer to be extended. Most preferred amounts of added centipede polymer include from about 0.5 to about 20 parts of centipede polymer per 100 parts of the elastomeric polymer. These parts by weight being effective plasticizing amounts of centipede polymer in elastomers.
Typical, but by no means limited to the types of thermodynamically miscible elastomeric polymers and copolymers that may be compatibly blended and extended by the centipede polymers of the present invention are elastomeric polymer containing formulations include but not limited to: natural rubber, polyisoprene, polybutadiene, butadiene/styrene rubber (SBR), ethylene/propylene copolymer rubbers and blends thereof. SBR and polybutadiene are preferred elastomers.
The use of poly(maleimide-co-alkenyl benzene) centipede polymers produced according to the present invention as plasticizers for elastomeric polymers either alone or as a partial oil substitute increases the damping properties of the elastomeric polymers over comparable oil extended polymers. The use of the centipede polymers as an extender in elastomeric polymers also increases the tensile strength, the maximum elongation, tear strength and the travel at tear characteristics versus elastomers extended with a comparable amount of oil extender.
Although the present invention also contemplates use of the instant centipede polymers in combination with conventional extender oils, an embodiment contemplates the total substitution of conventional extenders by centipede polymers. Typical prior art extenders replaced by the instant centipede polymers include extender oils and low molecular weight compounds or components. Such extender oils include those well known in the art such as naphthenic, aromatic and paraffinic petroleum oils and silicone oils. Examples of low molecular weight organic compounds or components extenders in the compositions that may be replaced by the centipede polymers of the present invention are low molecular weight organic materials having a number-average molecular weight of less than 20,000, preferable less than 10,000, and most preferably less than 5,000. Although there is no particular limitation to the material that the instant centipede polymers replace in prior art rubber compounds, the following is a list of examples of appropriate replaceable materials: (1) softening agents, namely aromatic, naphthenic and paraffinic oil softening agents for rubbers or resins; and (2) plasticizers, namely plasticizers composed of esters including phthalic, mixed phthalic, aliphatic dibasic acid, glycol, fatty acid, phosphoric and stearic esters, epoxy plasticizers, other plasticizers for plastics; and (3) petroleum hydrocarbons, namely synthetic terpene resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic or alicyclic petroleum resins, aliphatic or aromatic petroleum resins, polymers of unsaturated hydrocarbons, and hydrogenated hydrocarbon resins. The instant centipede polymers can be used to replace or partially replace one or more or all of these extender materials.
Additives useful in the compositions of the present application as well known in the rubber art. Stabilizers, antioxidants, conventional fillers, reinforcing agents, reinforcing resins, pigments, fragrances and the like are examples of some such additives. Specific examples of useful antioxidants and stabilizers include 2-(2xe2x80x2-hydroxy-5xe2x80x2-methylphenyl) benzotriazole, nickel dibutyldithiocarbamate, zinc dibutyl dithiocarbamate, tris(nonylphenyl) phosphite, 2,6-di-t-butyl-4-methylphenol and the like. Exemplary conventional fillers and pigments include silica, carbon black, titanium dioxide, iron oxide and the like. These compounding ingredients are incorporated in suitable amounts depending upon the contemplated use of the product, preferably in the range of 1 to 350 parts of additives or compounding ingredients per 100 parts of the elastomeric polymer.
A reinforcement may be defined as the material that is added to a the elastomeric compositions to improve the strength of the centipede extended elastomeric polymer. Most of these reinforcing materials are inorganic or organic products of high molecular weight. Various examples include glass fibers, asbestos, boron fibers, carbon and graphite fibers, whiskers, quartz and silica fibers, ceramic fibers, metal fibers, natural organic fibers, and synthetic organic fibers. Other elastomers and resins are also useful to enhance specific properties like damping properties, adhesion and processability. Examples of other elastomers and resins include adhesive-like products including Reostomer (produced by Riken-Vinyl Inc.), hydrogenated polystyrene-(medium or high 3,4) polyisoprene-polystyrene block copolymers such as Hybler (produced by Kurare Inc.), polynorbornenes such as Norsorex (produced by Nippon Zeon Inc.) and the like.
The centipede extended elastomer compositions obtained using the manufacturing method of this invention can be molded with equipment conventionally used for molding thermoplastics. These centipede extended elastomer compositions are suitable for extrusion molding, calendar molding, and particularly injection molding. These compositions can be mixed in any conventional mixer such as a Brabender mixer, a Banbury mixer or roll mill or extruder normally conducted within the temperature range of about 100xc2x0 C. to about 300xc2x0 C., preferably maintaining the composition above its melting point for a few minutes up to several hours, preferably 10 to 40 minutes. A particularly useful technique is to add any fillers in the beginning of the mixing cycle in order to take maximum advantage of heating time and to prevent surface bleeding and overheating when forming the molded articles.
The centipede extended elastomeric polymer formulations may be molded in appropriate press ovens and the like to form products in the form of extruded pellets, cut dices, preferably as small as possible since smaller pellets provide short heating times and better flow when utilized in flow molding. Ground pellets may also be utilized.
In summary, the poly(maleimide-co-alkenyl benzene) centipede extended elastomeric polymer formulations of the instant invention can be used in high temperature applications including uses in injection molding or in any other compositions typically for elastomeric properties. The use of the centipede polymers as an extender in elastomeric polymers increases the tensile strength, the maximum elongation, tear strength and the travel at tear characteristics versus elastomers extended with a comparable amount of oil extender.
Damping is the absorption of mechanical energy by a material in contact with the source of that energy. It is desirable to damp or mitigate the transmission of mechanical energy from, e.g., a motor, engine, or power source, to its surroundings. Elastomeric materials are often used for this purpose. It is desirable that such materials be highly effective in converting this mechanical energy into heat rather than transmitting it to the surroundings. It is further desirable that this damping or conversion is effective over a wide range of temperatures and frequencies commonly found near motors, automobiles, trucks, trains, planes, and the like.
A convenient measurement of damping is the determination of a parameter called tan xcex4. A forced oscillation is applied to a material at frequency f and the transmitted force and phase shift are measured. The phase shift angle delta is recorded. The value of tan xcex4 is proportional to the ratio of (energy dissipated)/(energy stored). The measurement can be made by any of several commercial testing devices, and may be made by a sweep of frequencies at a fixed temperature, then repeating that sweep at several other temperatures, followed by the development of a master curve of tan xcex4 vs. frequency by curve alignment. An alternate method is to measure tan xcex4 at constant frequency (such as at 10 hz) over a temperature range. We have defined an unfilled material as useful for damping when tan xcex4 greater than xcx9c0.3 over at least a 4 decade range, preferably a 6 decade range of frequency.
It is further important that this high degree of absorption of energy be accompanied by good mechanical and thermal stability, as the part prepared from the subject centipede extended polymers will be cycled through various environments and repeatedly such to various forces of compression, tension, bending, and the like.
The compositions of the present invention are favorably used in the manufacturing of any product in which the following properties are advantageous: a high degree of softness, heat resistance, decent mechanical properties, elasticity and/or high damping. The compositions of the present invention can be used in all industry fields, in particular, in the fabrication of automotive parts, tire tread rubbers, household electrical appliances, industrial machinery, precision instruments, transport machinery, constructions, engineering, and medical instruments.
Representative examples of the uses of the instant centipede extend elastomeric polymers are damping materials, and vibration restraining materials. These uses involve connecting materials such as sealing materials, packing, gaskets and grommets, supporting materials, such as mounts, holders and insulators, and cushion materials such as stoppers, cushions, and bumpers. These materials are also used in equipment producing vibration or noise and household electrical appliances, such as in air-conditioners, laundry machines, refrigerators, electric fans, vacuums, driers, printers and ventilator fans. Further, these materials are also suitable for impact absorbing materials in audio equipment and electronic or electrical equipment, sporting goods and shoes.
In the following, the present invention will be described in more detail with reference to non-limitative examples. The following examples and tables are presented for purposes of illustration only and are not to be construed in a limiting sense.